Systems that include rotating units require a power coupling device for coupling power to the electronic components within these rotating units. For example, when using CT scanners, it is necessary to supply power to the electronics on the rotating gantry, using a power coupling device. Traditionally, these power coupling devices have been slip-ring/brush assemblies. Slip-rings transfer electricity between a stationary member and a rotating member, through the contact of two materials, i.e. via a sliding contact. Slip-ring assemblies typically include two or more continuous conducting rings, and one or more brushes on each ring for delivering current to and from the rings.
Typically, numerous slip-rings must be used, in order to supply many different voltage levels, as required by the various electronic components of the rotating units. Conventional brush and slip-ring mechanisms tend to be dirty, unreliable, and noisy. Electric noise generation can cause interference with sensitive diagnostic procedures, such as CT imaging. Maintenance can be a significant problem, and the wearable components must be periodically replaced. These components can be converted to metallic dust, which may cause problems with ultra-sensitive electronics. Other drawbacks of slip-ring assemblies include the cost and complexity of manufacture, due to the special materials and the mechanical precision that are required.
A number of prior art references disclose inductive power coupling devices that allow power to be coupled to rotating systems, such as CT scanners, without using slip-rings. For example, U.S. Pat. No. 4,323,781 to Baumann discloses an inductive transformer for transmitting energy to the x-ray tube in a rotatable CT-scanning system. The inductive transformer in the Baumann patent consists of primary and secondary windings. An alternating current passing through the primary winding induces a current in the secondary winding. The primary winding is stationary with respect to the scanning system, whereas the secondary winding rotates with the scanning system, and provides power to the rotating x-ray tube.
U.S. Pat. No. 4,912,735 to Beer discloses a similar concept, namely a power transfer apparatus including two concentric rings mounted on a static member and a rotating member, respectively. The rings have opposed annular faces, each containing a groove. Conductive windings in each groove provide an inductive coupling means for coupling power to the rotating unit in the CT scanner. U.S. Pat. No. 5,608,771 to Steigerwald applies a substantially similar concept to a quasi-resonant high voltage generation scheme.
Although the devices discussed above allow for power transfer to rotating systems, without the need for sliding contacts and ensuing inconveniences, they suffer from a number of drawbacks. For example, these prior art devices do not provide to the user the flexibility of transferring power between a plurality of input and output voltages, as is necessary in many rotating systems such as CT scanners. For example, the user of a large CT system may need to derive many different voltages, at a relatively low power, for components on both the rotating and the stationary gantries of the CT system. However, the prior art power coupling devices discussed above do not provide such flexibility. Also, these prior art devices provide few options to the user for optimizing the current and voltage in the power transfer device, so as to achieve the best power transfer efficiency. Finally, none of these patents discuss the problem of shielding, which is a significant difference between inductively coupled systems and mechanical slip rings which are typically constant voltage devices.
For these reasons, there is a need for a more efficient power coupling device for rotating systems, which enables the user to transfer power between multiple voltages, as desired, and enables the user to optimize the current and voltage in the power coupling device, in order to achieve an optimum transfer efficiency. It is also desirable to provide an effective shielding mechanism.